It’s like a direct violation of Article I, Section 9 of the United States Constitution:

No bill of attainder or ex post facto Law shall be passed.,

Was it legal when they did it? Yes? Then penalizing them for having done it, whether via a retroactive criminal law (outright unconstitutional) or a retroactive tax penalty (which may have more flexibility in practice, though it shouldn’t in theory), is a violation of one of the first principles of the rule of law: that the law should be KNOWABLE.

A guy buys a house that is crumbling down, but he wants to save it. So he goes out and tries to find some people to fix the house. Trouble is, no one really wants to fix it. The house is falling apart and it would be cheaper to let it fall down and build up whatever is left standing. But the guy is adamant and wants to prop up the house, so he hires you to fix it. You’ll get paid, of course, and given a blank check – spend as much as you want. Also, if you do a good job, you’ll get a ham sandwich – it’s part of the contract. After six months and billions of dollars, the guy turns around and wants to know what you did with the ham sandwich. He’s mad that he gave you a ham sandwich. He’s going to charge you for that damn sandwich.